This invention pertains to intrusion detection systems, particularly intrusion detection systems which utilize a segmented sensor or plurality of sensors which are sensitive to both seismic and magnetic disturbances in distinct segments of a boundary.
Prior art intrusion detection systems have typically used either a series of seismic point sensors or a single magnetic line sensor to detect intrusion. An example of a system using geophones as seismic point sensors is shown in U.S. Pat. application Ser. No. 262,888, filed June 14, 1972 now U.S. Pat. No. 3,818,471. The information available from such systems is limited, and failure of these systems to provide sufficient intelligence to distinguish between noise, far-field disturbances and actual intrusions may result in nuisance alarms.
An example of a segmented sensor which can be used to provide both magnetic and seismic signals is shown in U.S. Pat. application Ser. No. 218,102, filed Jan. 17, 1972 now U.S. Pat. No. 3,747,036. The present invention is apparatus which will effectively use magnetic and seismic information from a plurality of boundary segments to gain information which decreases the probability of nuisance alarms while increasing the probability of detecting actual intrusions. The present invention is therefore particularly suited for use with a sensor of the type shown in application Ser. No. 218,102.
Two drawbacks of prior art systems have been: (i) their failure to accurately sense the lack of localization of a disturbance and inhibit intrusion alarm when the disturbance is not sufficiently localized to represent an intrusion, and (ii) their failure to use information about the impulsive or non-impulsive character of the disturbances to vary the level of disturbance required to activate the alarm.
It is therefore a principal object of the present invention to provide intrusion detection apparatus which detects whether or not a disturbance is localized and inhibits the alarm if the disturbance is not sufficiently localized to represent human intrusion.
Another important object is to provide intrusion detection apparatus which determines whether a detected seismic disturbance is impulsive in nature and uses the determination to vary the threshold of magnetic disturbance required to actuate an alarm.
Still another object is to provide an improved intrusion detection system usable with signals indicative of both seismic and magnetic disturbances.
Yet another object is to provide an improved intrusion detection system which utilizes signals indicative of the level of disturbances in a number of distinct segments of a boundary.